Serial digital pulse phase interface driver and receiver

ABSTRACT

A digital transmission system comprising a transmitter and receiver capable of transmitting and receiving digital data at high bit rates in a noisy environment, utilizing transformer coupling to a single transmission line, serial to parallel and parallel to serial conversion, and parity generation and checking circuits. The system is capable of operation from a 5 volt source and of being densely packaged. The serial digital receiver utilizes a decoding and filtering circuit which provides high noise immunity for the system. Data transmitted and received is in the form of pulses having a positive and negative peak so as to eliminate the necessity of a separate syne line.

United States Patent Griffin 1 July 25, 1972 [s41 SERIAL DIGITAL PULSE PHASE 2,s9|,|7o 6/1959 Paull ..340/l67 x INTERFACE DRIVER AND RECEIVER 2,985,716 5/1961 Day ..340/l67 x [72] Inventor: Jon ll. Grillin, Rockville, Md. Primary Examiner Hamld L Pins [73] Assignee: General Electric, Westlynn, Mass. Attorney-R. S. Sciascia and Thomas 0. Watson, Jr.

[22] Filed: July 10, 1970 [57] ABSTRACT [21] Appl' 53751 A digital transmission system comprising a transmitter and receiver capable of transmitting and receiving digital data at [52] U.S.Cl ..340/l67 R, 340/ 1688 high bit rates in a noisy environment, utilizing transformer [51] Int-Cl. q coupling to a single transmission line, serial to parallel and Field of Search SR, l67, l70 arallel to serial conversion and parity generation and checking circuits. The system is capable of operation from a 5 References Clled volt source and of being densely packaged. The serial digital receiver utilizes a decoding and filtering circuit which pro- UNITED STATES PATENTS vides high noise immunity for the system. Data transmitted 2,977,4l7 3/196] Doelz ..340/l68 SR and received is in the form of pulses having a positive and 3,009,136 1961 SR negative peak so as to eliminate the necessity of a separate 3,271,517 9/l966 De Rosa.... ..340/168 SR syneline. 2,545,349 3/]951 v Foster ..340/167 X 2,881,410 4/1959 Brunn ..340/167 X 9 Chins, 11 Drawing Figures DATA IN 22 28 {y' 25 27 2/ SHIFT 37 DRIVE GATED C 3 2 3 T 24 A OSCILLATOR 91 L31 T0 3/ c2 5:

31 PARITY To 34 GENERATOR 30 r 1* (:1 To c2 CON T ROL COUNTER PATENTEDJMS I972 SHEET 2 OF 4 P'ATE'N'TEDamzs m2 3.600.050

SHEET 3 UF 4 agATA omeg 65 63 27 \T TIME 1 $H|FT 7/ 0L wmoow 66 REGISTER easse'r FILTER 7/ 72 6 r 2 0ATA RECEIVED 68 64 PARITY 73 CHECK 3 1mg; OUTPUT ENABLE 651 P66 DATA OUT FIG. 7

+sv ms fiewmv //7 1/4 /20 65 OSI DATA 0S2 CLOCK FIG. 8

SERIAL DIGITAL PULSE PHASE INTERFACE DRIVER AND RECEIVER STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION The present invention relates generally to improvements in serial digital transmission systems, and more particularly, pertains to a new and improved interface driver and receiver in such systems wherein transformer coupling to the transmission line, high noise immunity, built in serial to parallel and parallel to serial conversation, integrated parity generation and parity checking, operation from a single volt power supply, and transmission on a single transmission line in the form of positive and negative pulses is provided. One of the more critical problems confronting developers of digital data transmission systems has been the coherent transmission of digital data at high bit rates in a noisy environment by means of a transmission system that is compact and capable of operating on low power supplies. These problems are overcome by the present invention.

SUMMARY OF THE INVENTION The system of the present invention has the capability of transmitting digital data at high bit rates (greater than 5 X bits per second) in a relatively noisy environment. The serial digital transmitter and the serial digital receiver employ transformers for coupling to the transmission lines. Built in serial to parallel and parallel to serial conversation and integrated parity generation and checking circuits are also used. The system is capable of operating from a single 5 volt power supply. In addition, the serial digital receiver has a decoding and filtering circuit that provides high noise immunity to the system. The building blocks of the system are capable of high packaging density, thus, providing for a very compact system.

The general purpose of this invention is to provide a digital data transmission system that has all the advantages of similarly employed transmission systems and has none of the above described disadvantages. To obtain this purpose, the present invention provides a unique digital data transmitter and digital data receiver, said receiver employing a decoding and filtering circuit which provides high noise immunity for the system.

OBJECTS OF THE INVENTION An object of the present invention is the provision of an improved serial digital data transmission system capable of transmitting data at high bit rates in a noisy environment.

Another object is to provide an improved serial digital transmission system capable of transmitting data at high bit rates in a noisy environment that requires only one transmission line.

A further object of the invention is the provision of an improved serial digital transmission system capable of transmitting data at high bit rates in a noisy environment that requires only one transmission line and is capable of operating from a 5 volt source.

Still another object is to provide an improved serial digital transmission system capable of transmitting data at high bit rates in a noisy environment that has built in serial to parallel and parallel to serial conversion and parity generation and checking circuits.

A still further object is to provide an improved serial transmission system having a transmitter and receiver capable of transmitting and receiving data at high bit rates in a noisy environment that utilize a decoding and filtering circuit in the receiver to provide high noise immunity.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a preferred embodiment of the digital data transmitter;

'FIG. 2 illustrates the gated three phase oscillator of the digital data transmitter of FIG. 1;

FIG. 3 illustrates the shift register of the transmitter of FIG.

FIG. 4 illustrates the various pulses that are generated by the components of the transmitter of FIG. 1;

FIG. 5 illustrates the driver logic and output section of the transmitter of FIG. 1;

FIG. 6 illustrates the various pulses that are generated by the driver logic of FIG. 5; 4

FIG. 7 illustrates a preferred embodiment of the digital data receiver of this invention;

FIG. 8 illustrates the time window filter of the digital data receiver of FIG. 7;

FIG. 9 illustrates the various signal states in the time window filter of FIG. 8;

FIG. 10 illustrates the various noise states in time window filter ofFIG. 8; and

FIG. 11 illustrates the shift register and output gating of the serial digital data receiver of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram illustration of the basic components in the digital data transmitter of the system. Shift register 22 is a 32 bit shift register which receives data at data input 28 in parallel form and converts it to a serial pulse train at output 36, 37. Gated three phase oscillator 21 has outputs 30, 31 and 32 which supply timing pulses to the various components of the transmitter. Control counter 23 controls the length of the transmit cycle, causes the data words to be transmitted to be loaded into shift register 22 and clocks in the parity bit at the end of each transmit cycle. Parity generator 24 generates a parity pulse at the end of each transmit cycle in response to a signal received from control counter 23. Driver logic 25 produces 5 volt bipolar pulses for application to the transmission line 27.

FIG. 2 represents the gated three phase oscillator 21 in combination with control counter 23. The three phase oscillator is comprised of a 15 MHz square wave oscillator 40 and a four state sequential logic circuit which has outputs C C and C on lines 30, 31 and 32 respectively. These outputs are produced by the oscillator 40 working in conjunction with the four state sequential logic circuit. The logic circuit comprises NAND gates 41, 42, 43, 44, 45, 46 and flip-flops 47, 48, and 49. All the NAND gates employed and all the flip-flops employed are 'ITL. Counter 23 is a control counter which consists of a module 33 counter, in other words has 33 states and two decoded outputs. The counter may be mechanized in any convenient fashion well known in the art.

With the aid of the pulse trains of FIG. 4 the operation of the three phase oscillator and control counter will now be explained. In its non-transmitting or quiescent state, three phase gated oscillator 21 has outputs C C and C on lines 30, 31, and 32 respectively which are all logic zero. If a logic one pulse is applied to terminal 20, which is the data transmit terminal, three phase gated oscillator 21 enters a cyclic mode generating a string of sequential pulses at its three outputs. Referring to FIG. 4, these outputs are illustrated at 30, 31 and 32. The outputs of oscillator 40 is illustrated as a pulse train 49. The data transmit pulse is illustrated at 20. The preferred embodiment is directed towards a transmitting system that can handle 32 bits. Therefore, the outputs 30, 31 and 32 of the three phase sequential oscillator continue in their cyclic mode for 32 cycles until the entire data word has been completely transmitted. At this time, the control counter output T illustrated at 34, returns to a logic zero. Output C at 30 is used to shift data out of shift register 22 and also to increment control counter 23. Outputs C, and C at 31 and 32 respectively are clock pulses that time the initial and final phases respectively of the transmitted serial pulse train. The data transmit pulse, illustrated at 20, must remain at a logic one throughout the transmit cycle and must be returned to a logic zero prior to output T of counter 22 switching to a logic zero. Output T of counter 23 is a logic zero upon initiation of three phase oscillator 21 and is a logic one at all other times. Output T -at 35, of counter 23 is a logic zero at bit time 31, and a logic one at all other times. This is clearly illustrated by pulse trains 34 and 35 respectively.

- Counter 23 may be cleared by the application of a logic zero at master clear line 29 at any time during the transmit cycle. The transmission system of this invention has been mechanized to transmit 30 bit data words. However, data words of any length can be accommodated by designing the appropriate number of bits into control counter 23 and shift register 22. In addition to the 30 data bits, two other bits must also be transmitted. The first bit transmitted is a logic one and is used as a control for the serial receiver. The last bit transmitted is a parity bit which may be optional and is generated by the parity generator 24.

FIG. 3 illustrates an embodiment of shift register 22 and parity generator 24 which may be employed in the invention.

During the nontransmit or quiescent state, when output T of counter 23 is a logic zero, parity generator 24 is set at zero and the preset enable inputof all the stages of the shift register is conditioned by way of gates N, and N,,. Upon pulse C being placed on line 30, the data word at input 28 is loaded into the shiftregister which is composed of serial registers SRIA to SRlH comprising 29 stages in all. A logic one is loaded into last stage P;, of the shift register by parity generator 24 so that the outputQ of the shift register is a logic one during the remaining portion of the time that the first pulse C is on line 30. The signal Q is transmitted as a pair of properly phased bipolar pulses when the second C pulse appears on line 30. The data in serial register 22 is shifted to the right and the first data bit of the data word is launched on the transmission line. This process continues until all 30 data bits have been transmitted. During this transmission process, parity generator 24 is toggled each time a logic one appears at output 37 of the shift register.'Therefore, if an odd number of ones have appeared on line 37 parity generator 24 will be reset.

During transmission of the last data bit, output T of counter 23 is a logic zero and the preset enable input of the shift register is again conditioned via gates N and N so that when parity bit generator 24 transmits the parity bit the shift register will be preset and output Q on line 37 will assume the complement of the stage of parity generator 24. Since this bit is transmitted during bit time 32, in other words the 32nd bit to be transmitted in the cycle, an odd number of ones is always transmitted (parity in essence being odd parity). At the termination of this last bit, time control counter 23 returns to its quiescent state as does the transmitter itself.

Driver logic 25, shown in FIG. 5, places bipolar pulses such as illustrated at 27 of FIG. 6 on transmission line 27. It consists of four driver gates which are 944 DTL power NAND gates. These driver gates N N are power bufi'ers and are connected as shown to a resistor and tap transformer. The output 0 and Q of shift register 22 are supplied to the four gates in conjunction with timing pulse trans C, and C on lines 31, 32, and 36, 37 respectively. As can be seen from the wave form diagrams of FIG. 6, the pulse trains C, and C on lines 31 and 32 are timing pulses that produce an output at point 52 and 53 of the driver logic circuit such as shown at lines 52 and 53 of FIG. 6. In response to the pulses in pulse trains 31 and 32 coinciding with output Q and Q of shift register 22 the pulses placed on transmission line 27 for each logic signal is a bipolar pulse such as shown at27 of FIG. 6.

Referring now to FIG. 7 which illustrates the serial digital 3 receiver of the system, it can be seen that the receiver is made up of three basic components, time window filter 61, shifl register 63 and parity check 62, and output gating 64;

FIG. 8 more specifically illustrates time window filter 6]. The pulses transmitted over transmission line 27 are introduced to the time window filter6l by way of a transformer which has a resistor R, coupled across its primary windings to terminate transmission line 27. Resistor capacitor combination 85, 86 and resistor capacitor combination 88, 87 function as single pole filters to provide high frequency attenuation to the received bipolar pulses. Two level thresholding is accomplished by the voltage base to emitter drop of transistors 92 and 93 in conjunction with the turns ratio of the input transformer. These two thresholds are set at approximately +1 volt and -l volt. Therefore, a logic zero at point 95 will correspond to an input signal in excess of IV, and a logic zero at point 96 will correspond to an input signal less than 1 volt. Both points, 95 and 96, will have a logic one for all input signals less than I volt and greater than I volt. The time window filter of FIG. 8 performs two functions. The first is to examine the time relationship between the positive and negative pulses on the transmission line in order to 10 ascertain whether a valid logic one or zero signal has been received. Secondly, the time window filter discriminates against all other signals and blocks those which do not correspond to the predetermined phase relationship of valid logic one and logic zero signals. The circuit accomplishes this byemploying a pair of one-shot multivibrators I01 and 102 that are cross coupled to establish timing windows. Resistor capacitor network 99,.

97 difi'erentiates the signal at point 95 such that a negative going spike is presented to the inverting input of one-shot multivibrator 101. Similarly, resistor capacitor network loo, 98 differentiates the wave form at point 96 such that a negative going spike is presented to the inverting input of one-shot multivibrator I02. Either one-shot multivibrator will be triggered by this spike if a logic one is also presented at its non-inverting input. The cross-coupling, therefore, will prevent eitheroneshot from being triggered when the other is in its stable state. Resistor capacitor network 105, I04 and I07, I06 establish the output pulse width of one-shot multivibrators 101 and 102 respectively. For a bit rate of 5 MHz a bit period of 200 nanoseconds is required which is divided into three equal 67 within time window filter 61, it can be seen that if a logic one signal for example, is being received at input 27, such as shown at 27 of FIG. 9, point 95 will go to a logic zero for 67' nanoseconds and trigger one-shot multivibrator 101 which thereby inhibits the triggering of one-shot multivibrator 102. Point 96 will then subsequently go to a logic zero for 67 nanoseconds as shown at 96 of FIG. 9. This logic zero at point 96 is inverted by NOT gate 109 and nanded with the output 11] of one-shot multivibrator 101 to produce a 67 nanosecond logic zero pulse at point 114, the output of NAND gate 117. In a similar fashion, if a logic zero signal is being received such, as the third signal on input line 27, point 96 will go to a logic zero for 67 nanoseconds and trigger oneshot multivibrator 102 which in turn inhibits the triggering of one-shot multivibrator 101. Point 95 will then go to a logic zero for 67 nanoseconds and this zero signal is inverted by gate I08 and nanded with output 112 of multivibrator 102 by 7 one pulses for every logic one and logic zero signal received.

They are illustrated at pulse train 65 and 66 of FIG. 9.

FIG. 10 illustrates the progression of noise through the time window filter. As can be seen from the figure, noise and all signals with improper phase and time relationship will produce no logic zero pulses at points 114 or .115 of the filter circuit because of the lack of time coincidence between the signals at point 95 and 96 with the signals generated by one-shot multivibrators 101 and 102 respectively.

Referring now to FIG. 11, which illustrates the shift register of the receiver, which performs the function of serial to parallel conversion, connected to the output gating and the parity checking circuit. The first bit of each word received is a control bit and a logic one. When this bit has been shifted into the last stage of shift register 63, it enables the data word in the shift register to be gated, by means of gates 79-81, to the output of the interface lines 70. At this point, the output of flipflop 62 can be examined. This flip-flop which is the parity check circuit is toggled for each logic one signal received and should be set at the end of the transmission of a word. It will be so set if an odd number of logic one signals have been received which is indicative of no one having occurred. Flip-flop 62 and shift register 63 is cleared by applying a logic zero pulse at reset line 71 prior to the reception of a subsequent data word. All four bit shift registers such as 75 and 76 are Fairchild 9300 and all gates such as 77, 78 and 79, 81 are DTL.

it can thus be seen that this invention provides an improved serial digital data transmission system that is capable of transmitting at high bit rates in a noisy environment and that it only requires one transmission line, is capable of operating from a 5 volt source, has built in serial to parallel and parallel to serial conversion, and parity generation and checking circuits, and utilizes a decoding and filtering circuit that provides high noise immunity. Various modifications are contemplated and may obviously be resorted to those skilled in the art without departing from the spirit or scope of the invention as hereinafter defined by the appended claims as only a preferred embodiment thereof has been disclosed.

What is claimed is: 1. In combination with a transmission system for transmitting and receiving digital data in the form of bits in a serial manner wherein the transmitting means receives the data to be transmitted in parallel form and converts it to series form before placing it on a transmission medium and the receiver means converts the data received into parallel form before delivering it to its output, the improvement which comprises:

driver logic means connected to the output of said transmitter means and to the transmission medium for generating, for each bit received from said transmitter, a bipolar pulse having positive and negative portions of equal amplitude and time and having a phase which is indicative of whether the bit received is a logic one or a logic zero; and

time window filter means connected to the transmission medium and said receiver means for receiving the bipolar pulses, examining the time relationship between the positive and negative portions of the pulses on the transmission line to determine whether a valid signal has been received, and examining the phase of a received valid signal to determine whether the signal represents a logic one or a logic zero.

2. The improved digital data transmission system of claim 1 wherein said driver logic means comprises:

four NAND gates connected together in parallel into first and second pairs; and

a transformer having its secondary winding connected to the transmission medium and having said NAND gates connected to its primary winding.

3. The improved digital data transmission system of claim 2 wherein said transformer comprises:

a primary winding with three taps, a first and second outside tap and a center tap, the first outside tap connected to the first pair of NAND gates and the second outside tap connected to the second pair of NAND gates, the center tap being connected to a power source.

4. The improved digital data transmission system of claim 2 wherein said time window filter means comprises:

a plurality of multivibrators connected to the transmission medium; and

logic circuit means connected to said multivibrators for delivering logic data and clock output pulses in response to said multivibrators.

5. The improved data transmission system of claim 4 wherein said multivibrators comprise:

a pair of one-shot multivibrators connected together in a cross-coupled manner.

6. A compact, low power transmission system for transmitting and receiving digital data in a serial manner, having a transmitter connected to one end of a transmission medium and a receiver on the other end of the transmission medium, said system comprising:

a transmitting shift register for receiving the data to be transmitted;

a control counter connected to said shift register for enabling said register so that the data to be transmitted is loaded into said register, and for controlling the length of the transmit cycle in response to the extent of loading of said shift register;

a parity generator connected to said shift register and said control counter, responsive to said control counter to generate a parity bit at the end of the transmit cycle;

driver logic means connected to said shift register, respon sive to the pulse output of said serial register to place bipolar pulses having positive and negative portions of predetermined time and phase relationship on the sending end of the transmission medium;

- a gated three phase oscillator connected to said shift register, control counter, parity generator and driver logic for supplying timing pulses to said shift register, contro counter, parity generator and driver logic; and

time window filter means connected to the receiving end of the transmission medium for decoding and filtering the received digital data by examining the time relationship of the positive and negative portions of the bipolar pulses and blocking all signals which do not correspond to the predetermined time relationship and by examing the phase relationship of the positive and negative the bipolar pulses to decode the data;

a receiving shift register connected to said time window filter means and responsive thereto to receive the decoded digital data;

output gating connected to said shift register fo'r removing data stored in said receiving shift register in response to an output enable signal;

a parity check circuit connected to said time window filter means, and said output gating for determining whether an error has occurred during transmission.

7. The transmission system of claim 6 wherein said logic means comprises:

four NAND gates connected together in parallel into first and second pairs; and

a transformer having its secondary winding connected to the transmission medium and having said NAND gates connected to its primary winding.

8. The transmission system of claim 7 wherein said time window filter means comprises:

a plurality of multivibrators connected to the transmission medium between the positive and negative pulses received on the transmission; and

logic circuit means connected to said multi-vibrators for delivering logic and clock output pulses in response to said multivibrators.

9. The transmission system of claim 8 wherein said multivibrators comprise:

a pair of one-shot multivibrators connected together in a cross-coupled manner.

portions of 

1. In combination with a transmission system for transmitting and receiving digital data in the form of bits in a serial manner wherein the transmitting means receives the data to be transmitted in parallel form and converts it to series form before placing it on a transmission medium and the receiver means converts the data received into parallel form before delivering it to its output, the improvement which comprises: driver logic means connected to the output of said transmitter means and to the transmission medium for generating, for each bit received from said transmitter, a bipolar pulse having positive and negative portions of equal amplitude and time and having a phase which is indicative of whether the bit received is a logic one or a logic zero; and time window filter means connected to the transmission medium and said receiver means for receiving the bipolar pulses, examining the time relationship between the positive and negative portions of the pulses on the transmission line to determine whether a valid signal has been received, and examining the phase of a received valid signal to determine whether the signal represents a logic one or a logic zero.
 2. The improved digital data transmission system of claim 1 wherein said driver logic means comprises: four NAND gates connected together in parallel into first and second pairs; and a transformer having its secondary winding connected to the transmission medium and having said NAND gates connected to its primary winding.
 3. The improved digital data transmission system of claim 2 wherein said transformer comprises: a primary winding with three taps, a first and second outside tap and a center tap, the first outside tap connected to the first pair of NAND gates and the second outside tap connected to the second pair of NAND gates, the center tap being connected to a power source.
 4. The improved digital data transmission system of claim 2 wherein said time window filter means comprises: a plurality of multivibrators connected to the transmission medium; and logic circuit means connected to said multivibrators for delivering logic data and clock output pulses in response to said multivibrators.
 5. The improved data transmission system of claim 4 wherein said multivibrators comprise: a pair of one-shot multivibrators connected together in a cross-coupled manner.
 6. A compact, low power transmission system for transmitting and receiving digital data in a serial manner, having a transmitter connected to one end of a transmission medium and a receiver on the other end of the transmission medium, said system comprising: a transmitting shift register for receiving the data to be transmitted; a control counter connected to said shift register for enabling said register so that the data to be transmitted is loaded into said register, and for controlling the length of the transmit cycle in response to the extent of loading of said shift register; a parity generator connected to said shift register and said control counter, responsive to said control counter to generate a parity bit at the end of the transmit cycle; driver logic means connected to said shift register, responsive to the pulse output of said serial register to place bipolar pulses having positive and negative portions of predetermined time and phase relationship on the sending end of the transmission medium; a gated three phase oscillator connected to said shift register, control counter, parity generator and driver logic for supplying timing pulses to said shift register, control counter, parity generator and driver logic; and time window filter means connected to the receiving end of the transmission medium for decoding and filtEring the received digital data by examining the time relationship of the positive and negative portions of the bipolar pulses and blocking all signals which do not correspond to the predetermined time relationship and by examing the phase relationship of the positive and negative portions of the bipolar pulses to decode the data; a receiving shift register connected to said time window filter means and responsive thereto to receive the decoded digital data; output gating connected to said shift register for removing data stored in said receiving shift register in response to an output enable signal; a parity check circuit connected to said time window filter means, and said output gating for determining whether an error has occurred during transmission.
 7. The transmission system of claim 6 wherein said logic means comprises: four NAND gates connected together in parallel into first and second pairs; and a transformer having its secondary winding connected to the transmission medium and having said NAND gates connected to its primary winding.
 8. The transmission system of claim 7 wherein said time window filter means comprises: a plurality of multivibrators connected to the transmission medium between the positive and negative pulses received on the transmission; and logic circuit means connected to said multi-vibrators for delivering logic and clock output pulses in response to said multivibrators.
 9. The transmission system of claim 8 wherein said multivibrators comprise: a pair of one-shot multivibrators connected together in a cross-coupled manner. 